Garage for Einzelabnahme (like TÜV) in Berlin ?

You seem to have some confusion about terms. The TÜV itself is an organization that inspects vehicles. They carry out the required safety inspection that is done on cars every 2 years (Hauptuntersuchen). It is just slang to say one got their "Tüv". The same organization does the Einzelabnahme which is a specialized inspection when a major change is made to a car or for a self-built one. Some garages also offer the official safety inspection (and possibly an Einzelabnahme) by bringing in an inspector from the TÜV. Same organization is ultimately inspecting the car.

The reason some garages do this, beyond the added fee, is to make it more convenient to local customers who might be far away from the TÜV installations (Prufstellen). They can also carry out small repairs like missing light bulbs etc. on the spot so that one does not have to return to get the safety sticker.

Basically, you just need to contact the nearest TÜV and make an appointment. Garages that arrange for TÜV inspection almost always advertise it. So if it is more convenient, you can a look around for a local garage and simply ask but expect to pay about 20% more than if you just take it to the TÜV yourself.

Here is a link to the TÜV in Berlin, they seem to have 13 location:

http://www.tuv.com/de/deutschland/aktuelles/berlin.jsp